A small size cartrideg for FET type electrolyte sensor is designed and faricated with much simplified process by using micromachining tenchiques such as silicon etching andglass bonding. Size of the whole cartideg is 2.4cm*2.5cm, and the dead volume of a micro flow-channel in the cartrideg is only 8.5.mu.l. The photosensitive polymer(THB 30) is used to define a micropool and to encapsulate the sensor surface for standardizationof electrolyte sensors. To miniaturize micro flow-channel conventional reference electrode(Ag/AgCl) a differential amplification is introduced using REFET and quasi reference electrode. Refet was fabricated using photosensitive polymer(OMR 83). The fabricated cartridge with built-in pH-ISFET showed good operational characteristics such as linearity and high sensitivity (55.4mV/pH) in a wide pH range(pH2-pH12).